1. Field of the Invention
The present invention relates to an air conditioning system and a method for operating the air conditioning system, and more particularly to an air conditioning system and a method for operating the air conditioning system, in which a plurality of compressors are simultaneously or selectively operated, based on the difference between a room temperature and a desired temperature generated during a waiting time for re-operation of the compressors.
2. Description of the Related Art
Generally, an air conditioner is an appliance in which a refrigerant passes through a compressor, a condenser, an expansion valve, and evaporator to establish a cooling cycle, thereby cooling a room.
The compressor included in such an air conditioner serves to compress a refrigerant circulating through an indoor or outdoor heat exchanger. In the case of a particular air conditioner, a direction change valve is also provided, in addition to such a compressor. The direction change valve is connected with a plurality of indoor and outdoor heat exchangers via refrigerant conduits, while being connected between the inlet and outlet of the compressor so as to change the circulating direction of a refrigerant, thereby causing the indoor heat exchangers to operate as warming or cooling units. In this case, therefore, it is possible for the air conditioner to more appropriately cope with both the environment of the room to be cooled and a desire of the user.
That is, the outdoor and indoor heat exchangers serve as a condenser and an evaporator, respectively, in a mode for cooling a room, while serving as an evaporator and a condenser, respectively, in a mode for warming the room. That is, the functions of the inner and outer heat exchangers are reversed in accordance with a change of the operating mode. Thus, different heat transfer cycles are established in accordance with different operating modes, respectively.
Such an air conditioner capable of performing both the cooling and warming functions is referred to as a xe2x80x9cheat pump type air conditionerxe2x80x9d. However, the following description relating to the present invention and related art will be given without limitation to any particular kind of air conditioners.
Generally, conventional air conditioning systems establish a cooling cycle adapted to condition indoor air, as shown in FIG. 1. Now, the conventional cooling cycle will be described in conjunction with FIG. 1.
The conventional cooling cycle includes a plurality of compressors 10 adapted to change a refrigerant from a low-temperature and low-pressure gaseous state into a high-temperature and high-pressure gaseous state. The compressors 10 are simultaneously or selectively operated to vary the capacity of the compressed refrigerant. In the illustrated case, two compressors, that is, first and second compressors 11 and 12, are used. In this case, both the first and second compressors 11 and 12 may operate simultaneously, or the first compressor 11 may operate while the second compressor 12 is maintained in a stopped state.
A direction change valve 20 serves to send, to an outdoor heat exchanger 50, a refrigerant emerging from the compressors 10 in a cooling mode, whereas it sends the refrigerant to indoor heat exchangers 30 in a warming mode. Thus, the direction change valve 20 changes the circulating direction of the refrigerant. The direction change valve 20 is used only in the case of heat pump type air conditioners having a cooling or warming function in order to establish a cooling or warming cycle in accordance with a flow of compressed refrigerant. In other words, general air conditioners for cooling purposes do not need such a direction change valve.
The outdoor heat exchanger 50 serves as condensing means for condensing the high-temperature and high-pressure gaseous refrigerant into a liquid state. This outdoor heat exchanger 50 constitutes an outdoor unit 99, along with an outdoor blower (not shown) installed at one side of the outdoor heat exchanger 50, and adapted to blow air toward the heat exchanger, thereby increasing the heat exchange efficiency of the heat exchanger. The outdoor blower includes an outdoor fan (not shown) and a motor (not shown).
The liquid refrigerant condensed by the condensing means is expanded into a low-temperature and low-pressure refrigerant of two phases, that is, gaseous and liquid phases in a mixed state, by an expansion member 40.
Each indoor heat exchanger 30 serves as evaporating means for externally absorbing heat, thereby changing the two-phase refrigerant into a gaseous state. An indoor blower (not shown) is installed at one side of each indoor heat exchanger 30 to discharge cooled air into a room. The indoor blower includes a motor 31 and an indoor fan 32. The indoor blower constitutes an indoor unit 39, along with the indoor heat exchanger 30. Thus, a cooling cycle of compression, condensation, expansion and evaporation is established.
In order for the cooling cycle of the above mentioned air conditioner to have a high efficiency, two compressors having different capacities, that is, the first and second compressors 11 and 12, are used. In the illustrated case, the first compressor 11 has a refrigerant compression capacity of 40%, whereas the second compressor 11 has a refrigerant compression capacity of 60%.
In the case of a high cooling load, both the first and second compressors are simultaneously operated in order to achieve a refrigerant compression rate of 100%. On the other hand, in the case of a low cooling load, only the first compressor is selectively operated to achieve a refrigerant compression rate of 40%. Thus, the refrigerant compression capacity of the air conditioner is variable.
FIG. 2 is a graph showing the operating states of a plurality of compressors included in a conventional air conditioning system. In the graph, the X-axis represents a compressor operation time, and the Y-axis represents a refrigerant compression capacity or compressor operation rate. FIG. 3 is a flow chart illustrating a conventional method for operating the conventional air conditioning system. Now, the conventional method for operating the conventional air conditioning system will be described in conjunction with the case in which two compressors are used.
First, the user sets a desired temperature after turning on the air conditioner (Step L1).
In order to reduce the temperature of a room to the set desired temperature, both the compressors are simultaneously operated two times (C1 and C2). That is, the room temperature reaches the desired temperature by eliminating the cooling load in the room by the 100% refrigerant compression capacity (Step L2).
When the room temperature reaches the desired temperature, the second compressor is stopped. That is, only the first compressor is selectively operated to carry out a cooling operation using a cooling cycle with a refrigerant compression capacity of 40% (C3) (Step L3).
The air conditioner senses the cooling load after the cooling operation. When the air conditioner senses elimination of the cooling load, it maintains the operating condition of the first compressor (C3). On the other hand, when the cooling load has not been eliminated yet, both the first and second compressors are operated (C4) so that the room temperature rapidly reaches a desired temperature (Step L4).
In accordance with the above mentioned operating method, the conventional air conditioning system operates to vary the refrigerant compression capacity of the compressors depending on the sensed cooling load under the condition in which one or more of the compressors are selectively operated. In order to re-operate any compressor maintained in a stopped state, however, a certain time is generally taken until pressure equilibrium is obtained between the refrigerant inlet and outlet of the compressor. This time is called a xe2x80x9cwaiting time for re-operationxe2x80x9d.
In conventional cases, in particular, conventional heat pump type air conditioners, the compression capacity of each compressor is determined without taking into consideration the amount of a cooling or warming load generated during the waiting time for re-operation. That is, any abrupt increase in cooling or warming load occurring during the waiting time for re-operation is not reflected upon controlling of compression capacity. For this reason, as such a cooling or warming load generated during the waiting time for re-operation is not eliminated, an abrupt increase or decrease in room temperature is caused. As a result, a degradation in the comfortableness of the room atmosphere occurs.
Therefore, the present invention has been made in view of the above mentioned problems involved with the related art, and an object of the invention is to provide an air conditioning system and a method for operating the air conditioning system, which are adapted to reflect, upon controlling the refrigerant compression capacity of a plurality of compressors, the amount of a cooling load generated during a waiting time for re-operation taken until each compressor maintained in a stopped state is re-operated by sensing the temperature of a room to be cooled, determining whether or not the difference between the sensed room temperature and a desired temperature set by the user is less than a predetermined value, and determining, based on the result of the determination, whether the compressors have to be simultaneously or selectively operated, thereby being capable of accurately determining the cooling load, and accurately controlling the operation of the compressors, and thus, achieving an improvement in the comfortableness of the room atmosphere.
In accordance with one aspect, the present invention provides an air conditioning system comprising: an air conditioner for establishing a cooling cycle adapted to sequentially perform compression, condensation, expansion and evaporation functions, and eliminating a cooling load in a room by the cooling cycle, thereby conditioning the atmosphere of the room; and a control unit for controlling an operation state of a compressor unit adapted to perform the compression function, in order to vary a refrigerant compression capacity of the compressor unit in accordance with the cooling load.
In accordance with another aspect, the present invention provides a method for operating an air conditioning system comprising the steps of: (A) simultaneously operating a plurality of compressors included in the air conditioning system until a temperature of a room to be cooled reaches a desired temperature; (B) stopping the operation of the compressors when the room temperature reaches the desired temperature, and sensing a temperature of the room after a waiting time taken until the stopped compressors are re-operated; and (C) simultaneously or selectively operating the compressors in accordance with a temperature difference between the room temperature sensed at the step (B) and the desired temperature.